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gefs: cleanly reject too many connections

before this commit, gefs would allow many attempts to
attach, but would blow up when we ran out of epoch ids;
now, we should log an error and reject the connection.

--- a/sys/src/cmd/gefs/blk.c

+++ b/sys/src/cmd/gefs/blk.c

@@ -849,6 +849,7 @@

 {

 	ulong ge;

+	assert(tid >= 0);

 	ge = agetl(&fs->epoch);

 	asetl(&fs->lepoch[tid], ge | Eactive);

 }

@@ -858,6 +859,7 @@

 {

 	ulong le;

+	assert(tid >= 0);

 	le = agetl(&fs->lepoch[tid]);

 	asetl(&fs->lepoch[tid], le &~ Eactive);

 }

--- a/sys/src/cmd/gefs/dat.h

+++ b/sys/src/cmd/gefs/dat.h

@@ -84,6 +84,7 @@

 	Leafspc 	= Blksz - Leafhdsz,

 	Msgmax  	= 1 + (Kvmax > Kpmax ? Kvmax : Kpmax),

 	Estacksz	= 64,

+	Maxprocs	= 128,

 };

 enum {

@@ -516,6 +517,7 @@

 	long	syncing;

 	long	nsyncers;

 	long	nreaders;

+	long	nprocs;

 	QLock	synclk;

 	Rendez	syncrz;

--- a/sys/src/cmd/gefs/fns.h

+++ b/sys/src/cmd/gefs/fns.h

@@ -64,7 +64,6 @@

 void	freeblk(Tree*, Blk*);

 void	freebp(Tree*, Bptr);

 int	logbarrier(Arena *, vlong);

-void	dlappend(Dlist *dl, Bptr);

 void	killblk(Tree*, Bptr);

 ushort	blkfill(Blk*);

 uvlong	blkhash(Blk*);

--- a/sys/src/cmd/gefs/main.c

+++ b/sys/src/cmd/gefs/main.c

@@ -189,26 +189,39 @@

 	}

 }

-static void

-launch(void (*f)(int, void *), void *arg, char *text)

+static int

+launch(void (*f)(int, void *), void *arg, long id, char *text)

 {

-	long pid, id;

+	long pid;

-	assert(fs->nworker < nelem(fs->lepoch));

+	assert(id == -1 || id < nelem(fs->lepoch));

+	if(aincl(&fs->nprocs, 1) >= Maxprocs){

+		werrstr("too many worker procs\n");

+		return -1;

+	}

 	pid = rfork(RFPROC|RFMEM|RFNOWAIT);

 	if (pid < 0)

-		sysfatal("can't fork: %r");

+		werrstr("fork: %r");

 	if (pid == 0) {

-		id = aincl(&fs->nworker, 1);

 		if((*errctx = mallocz(sizeof(Errctx), 1)) == nil)

 			sysfatal("malloc: %r");

 		(*errctx)->tid = id;

 		procsetname("%s.%ld", text, id);

 		(*f)(id, arg);

+		aincl(&fs->nprocs, -1);

 		exits("child returned");

 	}

+	return pid;

 }

+/* launches a proc that must start, kills the file system if it fails */

+static void

+xlaunch(void (*f)(int, void*), void *arg, long id, char *text)

+{

+	if(launch(f, arg, id, text) == -1)

+		sysfatal("setting up initial proc set failed: %r");

+}

+

 static int

 postfd(char *name, char *suff, int mode)

 {

@@ -255,7 +268,10 @@

 			close(fd);

 			continue;

 		}

-		launch(runfs, c, "netio");

+		if(launch(runfs, c, -1, "netio") == -1){

+			fprint(2, "listener failed: %r");

+			putconn(c);

+		}

 	}

 	close(actl);

 }

@@ -411,25 +427,25 @@

 		fs->arenas[i].sync = &fs->syncq[i%fs->nsyncers];

 	srvfd = postfd(srvname, "", 0666);

 	ctlfd = postfd(srvname, ".cmd", 0600);

-	launch(runcons, (void*)ctlfd, "ctl");

-	launch(runmutate, nil, "mutate");

-	launch(runsweep, nil, "sweep");

-	launch(runtasks, nil, "tasks");

+	xlaunch(runcons, (void*)ctlfd, aincl(&fs->nworker, 1), "ctl");

+	xlaunch(runmutate, nil, aincl(&fs->nworker, 1), "mutate");

+	xlaunch(runsweep, nil, aincl(&fs->nworker, 1), "sweep");

+	xlaunch(runtasks, nil, aincl(&fs->nworker, 1), "tasks");

 	for(i = 0; i < fs->nreaders; i++)

-		launch(runread, fs->rdchan[i], "readio");

+		xlaunch(runread, fs->rdchan[i], aincl(&fs->nworker, 1), "readio");

 	for(i = 0; i < fs->nsyncers; i++)

-		launch(runsync, &fs->syncq[i], "syncio");

+		xlaunch(runsync, &fs->syncq[i], aincl(&fs->nworker, 1), "syncio");

 	for(i = 0; i < nann; i++)

-		launch(runannounce, ann[i], "announce");

+		xlaunch(runannounce, ann[i], -1, "announce");

 	if(srvfd != -1){

 		if((c = newconn(srvfd, srvfd, -1)) == nil)

 			sysfatal("%r");

-		launch(runfs, c, "srvio");

+		xlaunch(runfs, c, -1, "srvio");

 	}

 	if(stdio){

 		if((c = newconn(0, 1, -1)) == nil)

 			sysfatal("%r");

-		launch(runfs, c, "stdio");

+		xlaunch(runfs, c, -1, "stdio");

 	}

 	exits(nil);

 }

-- 

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